Remove unused Lua functions

Author: tarleb

src/resources/filters/common/table.lua

@@ -46,13 +46,6 @@ function tcontains(t,value)
   return false
 end
 
--- clear a table
-function tclear(t)
-  for k,v in pairs(t) do
-    t[k] = nil
-  end
-end
-
 -- get keys from table
 function tkeys(t)
   local keyset=pandoc.List({})